1. Field of the Invention
The present invention relates to a device for controlling an aspect ratio in a TV-monitor integrated wide screen receiver. Specifically, this invention is a device for preventing horizontal distortion of a 4.times.3 picture displayed on a 16.times.9 wide screen monitor by controlling a sampling clock speed with a phase-locked loop system.
2. Discussion of Related Art
Conventionally, a monitor is similar to a TV receiver from which an antenna unit for receiving waves from a broadcasting station and a tuner unit for processing the waves from a TV receiver are removed. Component video signals and synchronous signals are transmitted to the monitor. The video signals are red (R), green (G), and blue (B) signals. The synchronous signals are horizontal (H) and vertical (V) signals. Composite video and synchronous signals are transmitted to the TV receiver. In a component method, horizontal and vertical frequencies of a picture are flexibly selected, so high resolution can be established. In a TV receiver, a signal band and horizontal and vertical deflection frequencies are determined according to known signaling systems such as NTSC, PAL, and SECAM. A composite method is limited in video signals, horizontal frequency, vertical frequency, video band, color carriers, and horizontal/vertical deflection frequencies so that it is not possible to freely choose frequencies.
Resolution indicates an amount of resolvable detail, and is expressed according to the number of dots or pixels which can be distinguished in a horizontal line and the number of lines which can be distinguished in a vertical frame and may be expressed as "DOT.times.LINE". For example, a resolution of 640 DOT.times.480 LINE indicates that the system has a horizontal resolution where up to 640 dots or pixels can be distinguished horizontally and a vertical resolution where up to 480 lines can be distinguished vertically.
Generally, in the United States, the NTSC television standard is set to have an aspect ratio of 4.times.3 (4:3), the ratio of frame width to frame height. FIG. 1A illustrates a screen whose width-height ratio is 4:3. Wide screen television usually will have an aspect ratio of 16.times.9 (16:9), and FIG. 1B illustrates a screen whose width-height ratio is 16:9. FIGS. 1C and 1D illustrate how a picture having a 4:3 aspect ratio may be displayed on a screen with an aspect ratio of 16:9, wherein the shaded areas are nonscanned areas of the cathode ray tube.
FIG. 2A shows an image displayed on a screen whose aspect ratio is 4:3. FIG. 2B shows a distorted image of a 4:3 aspect ratio picture displayed on a screen having the 16:9 aspect ratio. FIG. 2C illustrates a picture having the 4:3 aspect ratio being displayed on a screen having a 16:9 aspect ratio and the shaded areas are nonscanned areas for preventing the displayed picture from being distorted.
Where a TV picture of the 4:3 aspect ratio as shown in FIG. 2A, is displayed on a wide screen TV of the 16:9 aspect ratio, the picture is distorted horizontally as shown in FIG. 2B. Where widths of the screens A and B are put as L1 and L2, respectively, and lengths or heights of the two screens are put as H1 and H2, respectively, if the lengths are the same (H1=H2), the ratio of two widths (L1:L2) becomes 3 to 4. To display the 4:3 picture on the 16:9 screen without an image distortion, therefore, the length of the picture must be corrected to be 3/4.times.L2.
U.S. Pat. No. 5,159,438 to Khosro M. Rabii entitled Aspect Ratio Conversion Of Television Display describes a conventional aspect ratio conversion (ARC) which is applied to video signals and a wide screen TV of 16:9. Video signals in the NTSC system have the 4:3 aspect ratio. The ARC patent is applied to a wide screen TV having an aspect ration of 16:9, where a TV picture of 4:3 is displayed on the wide TV screen of 16:9. In a conventional art, a filter is used for an interpolation after an analog/digital conversion of luminance and chrominance signals, and another filter is used for a compressing method utilizing a difference between memory read and write clock speeds. In the NTSC system, synchronous signals (SYNC) and frequency modulated signals are mixed and then transmitted together through space, and the video signal has a horizontal frequency of 15.75 KHz, and a vertical frequency of 60 fields or 30 frames per second. The conventional art possibly processes signals only in NTSC system so that it cannot be applied to a computer system using a wide display.